<!DOCTYPE html>
<html lang="en">
<head>
  <!-- Required meta tags -->
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">

  <!-- Bootstrap CSS -->
  <link rel="stylesheet" href="./css/bootstrap.css">
  <style>
    .card-deck{
      /*background: #000000;*/
      /*margin-bottom: 2rem;*/
    }
    .row div{
      background: #399;
      border:1px solid #000000;
    }
  /*.carousel{
    background: #399;
    !*height:10%;*!
    max-height:20rem;
  }
    .carousel .carousel-inner .carousel-item{
      max-height:20rem;
    }*/
  </style>
</head>
<body>
<!--翻页 -->
<div class="mx-auto" style="width: 200px;">
  Centered element
</div>

<div class="container">
  <div class="row">
    <div class="col m-0 p-0">x
    </div>
    <div class="col p-3">xx
    </div>
    <div class="col px-1">xxx
    </div>
    <div class="col mx-1 m-0 p-5">xxx
    </div>
  </div>
</div>

<div class="visible">...</div>
<div class="invisible">xxx</div>

<script src="https://cdn.bootcss.com/jquery/3.2.1/jquery.slim.min.js"></script>
<script src="https://cdn.bootcss.com/popper.js/1.11.0/umd/popper.min.js"></script>
<script src="./js/bootstrap.js"></script>

</body>
</html>